[PATCH 4.9 1/1] tcp: refine memory limit test in tcp_fragment()

Greg Kroah-Hartman
2019-06-26T08:45:50Z

From: Eric Dumazet <edumazet@google.com>

commit b6653b3629e5b88202be3c9abc44713973f5c4b4 upstream.

tcp_fragment() might be called for skbs in the write queue.

Memory limits might have been exceeded because tcp_sendmsg() only
checks limits at full skb (64KB) boundaries.

Therefore, we need to make sure tcp_fragment() wont punish applications
that might have setup very low SO_SNDBUF values.

Fixes: f070ef2ac667 ("tcp: tcp_fragment() should apply sane memory limits")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Christoph Paasch <cpaasch@apple.com>
Tested-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/ipv4/tcp_output.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1185,7 +1185,7 @@ int tcp_fragment(struct sock *sk, struct
if (nsize < 0)
nsize = 0;

- if (unlikely((sk->sk_wmem_queued >> 1) > sk->sk_sndbuf)) {
+ if (unlikely((sk->sk_wmem_queued >> 1) > sk->sk_sndbuf + 0x20000)) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPWQUEUETOOBIG);
return -ENOMEM;
}